Fast-charging, high-capacity energy storage devices, such as supercapacitors and lithium (Li) ion batteries, are used in a growing number of applications, including portable electronics, medical devices, transportation, grid-connected large energy storage, renewable energy storage, and uninterruptible power supplies (UPS). In modern rechargeable energy storage devices, the current collector is made of an electric conductor. Examples of materials for the positive current collector (the cathode) include aluminum, stainless steel, and nickel. Examples of materials for the negative current collector (the anode) include copper (Cu), stainless steel, and nickel (Ni). Such collectors can be in the form of a foil, a film, or a thin plate, having a thickness that generally ranges from about 6 to 50 μm.
The active electrode material in the positive electrode of a Li-ion battery is typically selected from lithium transition metal oxides, such as LiMn2O4, LiCoO2, LiNiO2, or combinations of Ni, Li, Mn, and Co oxides, and includes electroconductive particles, such as carbon or graphite, and binder material. Such positive electrode material is considered to be a lithium-intercalation compound, in which the quantity of conductive material is typically in the range from 0.1% to 15% by weight.
Graphite is usually used as the active electrode material of the negative electrode and can be in the form of a lithium-intercalation meso-carbon micro beads (MCMB) powder made up of MCMBs having a diameter of approximately 10 μm. The lithium-intercalation MCMB powder is dispersed in a polymeric binder matrix. The polymers for the binder matrix are made of thermoplastic polymers including polymers with rubber elasticity. The polymeric binder serves to bind together the MCMB material powders to manage crack formation and disintegration of the MCMB powder on the surface of the current collector. The quantity of polymeric binder is typically in the range of 0.5% to 30% by weight.
The separator of Li-ion batteries is typically made from microporous polyolefin polymer, such as polyethylene foam, and is applied in a separate manufacturing step.
As Li-ion batteries become more important for power applications, cost-effective, high-volume manufacturing methods are needed. The electrodes of Li-ion batteries are commonly made using a sol gel process in which a paste of battery active material is applied to a substrate as a thin film and then dried to produce a final component. CVD and PVD processes are also conventionally used to form battery active layers for thin film batteries. Such processes have limited throughput, however, and are not cost-effective for high volume manufacturing.
Accordingly, there is a need in the art for cost-effective, high volume methods for making Li-ion batteries, and new materials suitable for such methods.